Differential coding of fruit, leaf, and microbial odours in the brains ofDrosophila suzukiiandDrosophila melanogaster

Abstract

ABSTRACTThe flyDrosophila suzukii, a close relative ofD. melanogasterseverely damages the production of berry and stone fruits in large parts of the world. UnlikeD. melanogaster, which reproduces on overripe and fermenting fruits on the ground,D. suzukiiprefers to lay its eggs in ripening fruits still on the plants. Flies locate fruit hosts by their odorant volatiles, which are detected and encoded by a highly specialized olfactory system before being translated into behaviour. The exact information processing pathway is not yet fully understood, especially the evaluation of odour attractiveness. It is also unclear what differentiates the brains ofD. suzukiiandD. melanogasterto cause the crucial difference in host selection. We hypothesized that the basis for different behaviours is already formed at the level of the antennal lobe ofD. suzukiiandD. melanogaster,by different neuronal responses to volatiles associated with ripe and fermenting fruit. We thus investigated by 3Din vivotwo-photon calcium imaging how both species encoded odours from ripe fruits, leaves, fermented fruits, bacteria, and their mixtures in the antennal lobe. We then assessed their behavioural responses to mixtures of ripe and fermenting odours. The neural responses reflect species-dependent shifts in the odour code. In addition to this, morphological differences were also observed. Yet this was not directly reflected in different behavioural responses to the odours tested.